The process of cancer progression, from normal cells to invasive and disseminated cells can be halted at many stages by therapeutic intervention. Combination therapy has been preferred for the treatment of most solid tumors as clinical trials suggested that there was improved disease-free survival and overall survival from the use of combination drug protocols. See Chabner, Cancer Chemotherapy, pp. 1-15, Lippencott; and DeVita, Cancer, Principles & Practice of Oncology, 3rd ed., pp 276-300, Lippencott. The basis for combination therapy may be either empiric, e.g. the use of several cytotoxic chemotherapeutic agents With potentially different mechanisms of action, or based upon laboratory demonstration of increased efficacy in vitro or in vivo.
Compound 1 is an inhibitor of calcium uptake through nonvoltage-gated and voltage-gated calcium channels. See. Felder, et al., J. Pharm. Exp. Therap., 257:967-971 (1991); and Hupe, et al., J. Biol. Chem. 266:10136-10142 (1991). Compound 1 has demonstrated antiproliferative, anti-invasive, and anti-metastatic properties as a single agent both in vitro and in vivo. See Kohn, et al., Proc. Natl. Acad. Sci. USA, in press; co-pending application U.S. Ser. No. 08/123,614, now abandoned, and its CIP U.S. Ser. No. 08/209,651 filed Mar. 10, 1994; Kohn et al., J. Natl. Cancer Inst. 82:54-60 (1990); Kohn, et al., Cancer Research, 52:3208-3212 (1992); and Kohn, et al., Cancer Research, 54:935-942 (1994). Human clinical trials using compound 1 are now in progress. ##STR1##
Compound 2 is another agent with selectivity for receptor-mediated calcium entry (RMCE). This compound inhibits RMCE in platelets, endothelial cells and neutrophils, and blocks voltage-gated L-type calcium channels in vascular smooth muscle cells under patch clamp. Merritt, et al., Biochem. J. 271:515-522 (1990).
Modulation of calcium homeostasii may have many downstream effects within the cell, either from alteration of secondary signalling pathways or direct effects on calcium-sensitive events within the cell. See Cole, et al., Cancer and Metastasis Reviews, 13:31-44 (1994). Compound 1 has been shown to alter production of arachidonic acid, a calcium-sensitive event. See Felder, et al., J. Pharm. Exp. Therap. 257:967-971 (1991), Kohn, et al., Cancer Research, 54:935-942 (1994) and Lin, et al., Cell 72:269-278 (1993). Additionally, compound 1 inhibits phosphorylation events which are associated with receptor activation. See Kohn, et al., Proc. Nat. Acad. Sci. USA in press; co-pending application U.S. Ser. No. 08/123,614, now abandoned, and its CIP U.S. Ser. No. 08/209,651 filed Mar. 10, 1994; and Gusovsky, et al., J. Biol. Chem. 268:7768-7772 (1993). A direct effect of compound 1 may also be seen at steps such as microtubule polymerization and stabilization, due to its modulation of cellular calcium. See Dinsmore, et al., Cell, 53:769-780 (1988); Pirollet, et al., Biochemistry, 31:8849-8855 (1992); and Zamansky, et al., J. Investigative Dermatology, 97:985-994 (1991).
Paclitaxel (Taxol.RTM.), compound 3, is a diterpene isolated from the bark of the Western (Pacific) yew, Taxus brevifolia and is representative of a new class of therapeutic agent having a taxane ring system. Paclitaxel and its analogs have been produced by partial synthesis from 10-deacetylbaccatin III, a precursor obtained from yew needles and twigs, and by total synthesis. See Holton, et al., J. Am. Chem. Soc. 116:1597-1601 (1994) and Nicolaou, et al., Nature 367:630 (1994). Paclitaxel has been demonstrated to possess antineoplastic activity. More recently, it was shown that the antitumor activity of paclitaxel is due to a promotion of microtubule polymerization. See Kumar, N., J. Biol. Chem. 256:10435-10441 (1981); Rowinsky, et al., J. Natl. Cancer Inst., 82:1247-1259 (1990); and Schiff, et al., Nature, 277:655-667 (1979). Paclitaxel has now demonstrated efficacy in several human tumors in clinical trials. See McGuire, et al., Ann. Int. Med., 111:273-279 (1989); Holmes, et al., J. Natl. Cancer Inst., 83:1797-1805 (1991); Kohn et al., J. Natl. Cancer Inst., 86:18-24 (1994); and Kohn, et al., American Society for Clinical Oncology, 12 (1993). ##STR2##
The role of signalling molecules and metal ions, specifically calcium, has previously been described for normal microtubule functioning. See Dinsmore, et al., Cell, 53:769-780 (1988); Pirollet, et al., Biochemistry, 31:8849-8855 (1992); and Zamansky, et al., Journal of Investigative Dermatology, 97:985-994 (1991). These observations suggest that low intracellular calcium might further stabilize microtubule polymerization.